Recently, there have been studies to install power generation facilities that use renewable energy without greenhouse gas emissions during power generation and achieve lower carbon in electric power supply systems. In power generation using renewable energy, the amount of electric power supply is more difficult to control than in power generation systems such as thermal power generation systems. Thus, stable supply of electric power is demanded.
For example, photovoltaic power generation varies in power generation amount in a long time or in a short time depending on the amount of insolation. It is therefore difficult for the photovoltaic power generation to achieve stable supply of electric power as compared with power generation systems such as thermal power generation systems. In order to solve such a problem, there have been suggestions made regarding conventional photovoltaic systems. One suggestion is to combine a power generation system with a power storage device such as a storage battery so that the total effective power of a photovoltaic power generation module and a power storage is controlled to provide fixed power. Another suggestion is a method of inhibiting a short-time fluctuation in the output of photovoltaic power generation.
However, a synchronous generator for, for example, thermal power generation is potentially provided with a function to inhibit a variation in system frequency, and comprises a governor so that in the even of a variation in system frequency, the amount of power generation is adjusted to inhibit the variation. This contributes to the stabilization of the system frequency. In contrast, the conventional photovoltaic system in which the solar power generation module is combined with the power storage device does not have the above-mentioned frequency adjustment function that is generated in the synchronous generator in the even of a variation in system frequency. It is therefore anticipated that if the photovoltaic systems are introduced in large numbers into an electric power system, the stabilization of the system frequency may be difficult.
On the other hand, each synchronous generator has its own operating characteristics including the function of inhibiting a variation in system frequency. The characteristics cannot be changed even if the conditions of a system to be connected change. Thus, the synchronous generator does not necessarily perform the optimum operation depending on the operating condition of the electric power system.